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Well, if the aperture blades are sticky ... that would prevent movement. There is a spring that returns the aperture back to its tightest position. It also could be SPRUNG, so to speak. Usually you will see the aperture blades visibly widen when you put on the rear lens cap (provided it has the blade actuator in it).

Last edited by DonSchap; 12-08-2009 at 04:27 PM.

Don Schap - BFA, Digital Photography A Photographer Is ForeverLook, I did not create the optical laws of the Universe ... I simply learned to deal with them.
Remember: It is usually the GLASS, not the camera (except for moving to Full Frame), that gives you the most improvement in your photography.flickr® & Sdi

Well, if the aperture blades are sticky ... that would prevent movement. There is a spring that returns the aperture back to its tightest position. It also could be SPRUNG, so to speak. Usually you will see the aperture blades visibly widen when you put on the rear lens cap (provided it has the blade accutator in it.

When I put on the rear lens cap and tighten it, the aperture blades goes visibly widen. But they stay that way, when I remove the lens cap, so there is no /is not enough force from the spring to return them back to smallest aperture.

I hope its enough to clean the iris blades to get it functioning again. However,
if the spring is damaged, where can I buy a new one?
/garda from Sweden

Your picture shows the Aperture Lever in the open position. It would normally be in the closed position.
Get one of your other lenses and move the lever to and fro to see how it feels against the resistance of the spring.
The comparison between the two should give you a good idea of whether the spring is the problem or not.

I have opened the lens from the back. A tiny small spring was found loose. It is probably the ground spring, that was mentioned by Peekayoh further back in this thread. See pictures: Attachment 50883Attachment 50882

On the second picture, the spring for minimizing the iris is fully functional (2550-1420-01), so I will open the lens from front-side to try cleaning the iris-blades. I think the loose spring has part number 2550-1424-01, as seen on this picture: http://www.pbase.com/pganzel/image/54100004 By inspection of that picture, I found where the ground spring shall be placed.

I have successfully cleaned the irisblades and now the lens is fully functional!

I lost the ground spring, but replaced with a bit of copper wire, as suggested in the comments of the tutorial I have previously linked to. Thanks to this thread and the tutorial, my lens is now working. Great.